Heretofore, a film of various metals such as Au, Ag and Pt and Cu; a film of metal oxides such as indium oxide doped with tin or zinc (ITO or IZO), zinc oxide doped with aluminum or gallium (AZO or GZO) and tin oxide doped with fluorine or antimony (PTO or ATO); a conductive film of nitrides such as TiN, ZrN and HfN and a conductive film of borides such as LaB6 and the like are well-known as transparent conductive electrodes, and further, various electrodes including a combination thereof such as Bi2O3/Au/Bi2O3 and TiO2/Ag/TiO2 and the like are well-known. In addition to the transparent electrodes described above, a transparent electrode employing CNT (carbon nanotube) or a conductive polymer has been also proposed (for example, refer to Non-Patent Document 1).
However, the films of metals, nitrides or borides described above and a conductive polymer film are utilized only in a specific technological field such as electromagnetic wave shielding or in a touch panel field when even a relatively high resistance is acceptable, since high optical transparency and high electroconductivity are incompatible.
On the other hand, a metal oxide film is predominantly utilized as a transparent electrode, since it has excellent durability and compatibility between high optical transparency and high electroconductivity. Particularly, ITO is often utilized as a transparent electrode for various optoelectronics application, since it has good balance between optical transparency and electroconductivity, and can easily form a fine electrode pattern according to a wet process employing a solution as well as a vacuum process such as sputtering. However, the vacuum process such as sputtering requires expensive equipment in order to form a transparent conductive film, while the wet process requires annealing treatment at high temperature of 500° C. or higher in order to obtain high electroconductivity.
Besides the transparent electrodes described above, there is proposed a transparent electrode with fine meshes composed of metal nanowires (for example, refer to Patent Document 1). Particularly, metal nanowires employing silver provide compatibility between high electroconductivity and high transparency, due to high electrical conductivity that silver itself has.
As a method of forming a transparent electrode pattern employing metal nanowires, there are mentioned a method employing a printing ink containing electroconductive microwires (for example, refer to Patent Document 2) and a method forming a nanowire pattern according to photolithography (for example, refer to Patent Documents 3 and 4).
However, in any methods as described above, electroconductivity lowers due to increase of contact resistance between the metal nanowires caused by a binder, and further, removal of the resist penetrating in the fine metal nanowire meshes may be insufficient, resulting in lowering of light transmittance, and on removal of the resist, metal nanowires are released. As described above, a conventional pattern formation method is not satisfactory.